Shielded resistor unit



Aug. 7, 1951 e. w. PACKER SHIELDED RESISTOR UNIT Filed Nov. 3, 1949 mmhum NW Wm Y M mm 6m Gm HIIIIII QVVENTOR. Glenn 14 Packer BY a ig ATTOQNE v Patented Aug. 7, 1951 SHIELDED RESISTOR UNIT Glenn W. Packer,Chica go, 111., assignor to Goodman ManuiacturinglsCompany, Chicago,Ill., a

corporation of Illino Application November 3, 1949, Serial No. 125,191

4 Claims.

This invention relates to an improved resistor of the kind used withheavy duty electric motors, as for example, with motors for electricmining locomotives which may be operated in explosive atmospheres.

Resistors for motors used in gassy mines must be completely shielded orenclosed to reduce the hazard of explosion. As a practical matter towithstand the shocks of rough usage, as well as to dissipate heatgenerated by the resistance unit, the shell or enclosure will usually bemade of metal such as steel. Enclosing the resistance unit greatlycomplicates the problem of heat dissipation, causing the resistance unitto run at a very high temperature at times, which in turn causes it todistort and may eventually lead to failure by shorting against the metalcase. In the'past, such failures have been tolerated as unavoidable inheavy duty equipment and replacement of resistor units at frequentintervals has been commonplace.

An object of the present invention, therefore, is to provide an improvedheavy duty resistor unit which is entirely enclosed for use in gassymines, yet which will dissipate heat rapidly enough to prevent failurethrough warping or distortion.

An important feature of the present invention is that the heatgenerating resistor element is resiliently mounted within the casing insuch a manner that the mounting will lend itself flexibly todistortional movements of the element during heating and cooling. Thisis a great improvement over conventional rigid mountings which tend tocrumble or break when the element is distorted.

Other objects and advantages will be apparent from the followingdescription taken in connection with the drawings in which:

Figure 1 is a longitudinal sectional view of one embodiment of ashielded resistor unit made in accordance with the present invention;

Fig. 2 is an outside end view of Figure 1;

Figure 3 is a sectional view of Figure 1, taken along the line 9-4 andFigure 4 is a fragmentary view similar to Fig ure 1, showing how themounting means for the resistance element may deflect to accommodatedistortion of the latter.

Referring now more specifically to the drawings, the embodimentillustrated comprises a casing generally designated 2| and consisting ofa tubular shell 22 and a pair of identical closure members 22. The shellwill preferably be of heat conductive material, such as steel; theclosure members will preferably be of brass. A shown in Figure 2, theclosure members are square in section and have at each corner a tie bolt24, effective to press the closure members tightly against the oppositeends of the shell.

To facilitate stacking multiple units, where more than one are required,aligning pins 26 and holes 21 are provided in opposite edges of thecover plates. Thus, multiple units may be stacked (and externallyinterconnected) to suit the requirements of a particular installation.Internally of the casing and protected thereby from the atmosphere, is aresistance element 29, in this case an iron coil. Each end is welded tothe outer edge of a steel washer 29, which in turn is welded to theunderside of the head of a steel electrode bolt 31. The shank 32 of theelectrode bolt is square (for instance, Figure 3) and is engaged withina star-shaped opening 33 in a washer 34. The star-shaped opening permitsa plurality, in this case eight, of rotative positions of the electrodebolt 3|. To maintain the washer 94 against rotation during tightening ofthe electrode bolt. its periphery is flattened in two places, as at 26,and these flats are engaged by a correspondingly formed seat 31 in aceramic insulating disc 38.

which is seated against the inner face of the end wall 23. An inwardlyextending peripheral skirt 3!, formed on each closure member, defines asocket for the corresponding disc 38. To prevent rotation of eachceramic disc 38 relative to its end wall, a pin 4| carried in the latterengages a slot 42 formed in the former.

Each electrode bolt 3| is electrically insulated from its correspondingclosure member and its washer 44, by means of a bushing 43 and anannular disc 46, the latter two members being made of a suitably heatresisting material, as for example, mica.

The electrodes are held fast in place by means of nuts 41. Terminals 48held on by nuts 49 may suitably connect the resistance coil element 28into an external circuit, as for example, the starting circuit of aseries motor in any well known manner.

At times in heavy duty service the resistance element 28 may actuallyrun at red heat. This may soften and distort the element so it sags,twists, and warps. An important feature of the present invention lies inthe improved means for resiliently supporting the resistance elementintermediate its ends and preventing it from shorting out against thesteel shell 22 under such conditions.

The improved supporting means for the resistance element 28 includes aplurality of elecascaaeo J 3 trically insulating elements Bil in thiscase ceramic rings disposed at intervals along the shell 22, each havinga central aperture 52 in which the resistance coil is supported.

The supporting elements are resiliently mounted at intervals along theaxis of the casing by resilient means, in this case coil springs 53,compressibly interposed between the end rings El and their correspondingclosure members 23, and between adjacent rings 5|, all as shown inFigure 1. The free length of the coil springs 53 will preferably begreater than their assembled length so they will normally be undercompression in the assembly, and their free diameter will preferably begreater than their assembled diameter so that they will normally pressoutward into contact with the shell 22 to facilitate heat dissipation.Normally, the springs 53 will run at a considerably higher temperaturethan the shell 22, and in order that they maintain a usable measure oftheir strength and resilience under operating conditions, they willpreferably be made of some heat resisting material such as stainlesssteel.

Figure 4 illustrates how, under severe warping conditions, theindividual ceramic supporting elements 5| will tilt to accommodatedistortion of the resistance element 28, instead' of cracking orchipping as would be the case if the supporting elements were rigidlymounted. To accommodate this desirable tilting, when needed, someclearance should be left between the elements 5! and the shell, as shownat 54 in Figure 1.

While one form of the improved resistor unit has been illustrated anddescribed, other modifications thereof will be apparent to those skilledin the art as falling within the scope of the invention as defined bythe appended claims.

I claim as my invention: I

1. A shielded resistor unit comprising a casing consisting of a tubularmetallic shell having closure members at opposite ends thereof, aresistance element extending along the interior of said casing,electrodes outside of said casing and means for connecting opposite endsof said resistance element to said electrodes, and means for supportingsaid resistance element intermediate its ends including at least onemember made of electrically insulating material tiltably supportedwithin said shell and itself supporting said resistance element out ofcontact with said shell, and resilient means effective to maintain saidmember at a predetermined position along the resistance element.

2. A shielded resistor unit comprising a casing consisting of a tubularheat conductive shell having closure members at opposite ends thereof, aresistance element extending along the interior of said shell,electrodes terminating outside of said casing and being connected toopposite ends of said resistance element; and supporting means for saidresistance element intermediate its ends including an electricalinsulating element disposed within said shell and embracing saidresistance'element to maintain the latter spaced from the shell, saidelectrically insulating element being resiliently urged to apredetermined disposition along the resistance element by resilientmeans reacting against at least one end of the casing, said resilientmeans being disposed in heat conducting relationship with said shellwhereby the latter will be efiective to dissipate heat absorbed by theresilient means from the resistance element when hot.

3. A shielded resistor unit comprising a casing consisting of a tubularheat conductive shell having closure members at opposite ends thereof,an elongated resistance element extending along the interior of theshell between the closure members, exterior electrodes connectedrespectively to opposite ends of said resistance element; and supportingmeans for said resistance element including a plurality of aperturedspacers of electrically insulating material each tiltably supportedwithin said shell at predetermined positions along the interior of saidshell and eifective to support said resistance element to maintain itout of contact with the shell, and metallic helicalshaped separatingmembers in heat-conductive contact with said shell and interposedbetween adjacent of said spacers and between the end spacers and theircorresponding closure members to retain the spacers in their saidpredetermined positions.

4. A shielded resistor unit comprising a casing consisting of a tubularheat conductive shell having closure members at opposite ends thereof, aresistance element extending along the longitudinal axis of the shellinteriorly thereof, exterior electrodes connected respectively toopposite ends of said resistance element; and supporting means for saidresistance element including a plurality of ceramic members tiltablysupported at intervals along the interior of the casing, each having anaperture embracing said resistance element to tilt with distortion ofthe latter and effective to maintain the latter out of contact with theshell, and a plurality of coil springs in heat-conductive contact withthe shell being compressibly interposed between the end ceramic membersand the corresponding ends of the casing and between adjacent ceramicmembers to maintain the latter resiliently disposed at their saidintervals along the interior of the casing.

GLENN W. PACKER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,154,417 Kuhn Sept. 21, 19151,963,328 Holinger June 19, 1934 2,397,291 Robertson Mar. 26, 1946

